The purpose of circuit breakers is to decouple a number of loads from a voltage supply system when a specific disturbance occurs. The classic disturbance is the occurrence of a short-circuit current, and the circuit breakers are conventionally designed to move a switching element in the event of a short-circuit current such as this, and thus to disconnect the connection between the loads and the power supply system.
However, the aim now is to disconnect loads in the power supply system in this way in other situations, as well. In particular, when disconnection of the power supply system from the loads in the event of an over voltage or an undervoltage in the power supply system is desired. Auxiliary tripping units are used to provide a functionality for this purpose. Such units are typically in the form of a withdrawable unit, which can be pushed into a withdrawable unit compartment in the circuit breaker. Part of the tripping mechanism in a circuit breaker is conventionally a latching mechanism. The auxiliary tripping units can act on this particular latching mechanism, thus producing the circuit breaker disconnection process. For this purpose, it is equipped with a tripping element, for example a plunger. The tripping element, that is to say in particular the plunger, is retracted in an untripped state. The tripping element moves out of a housing of the auxiliary tripping unit for tripping.
After tripping, it must be possible to reset the system. A circuit breaker has a handle for resetting, which acts on the latching mechanism. This handle is also used to reset the auxiliary tripping unit. It is therefore normal for the latching mechanism of the circuit breaker to act indirectly on the tripping element when the circuit breaker handle is operated.
There is a chain of action in an auxiliary tripping unit: There are monitoring means which identify tripping, in particular by monitoring the voltage and thus identify that a voltage threshold value has been overshot or undershot. There is an armature which can be moved by movement means, and these movement means are driven by the monitoring means when tripping occurs. The armature typically does not act directly on the tripping element, but is coupled to it via a moving body. One reason for this, inter alia, is that it is easier to reset the tripping element as well as the armature via the moving body.